Many electronic devices require more than one direct current constant voltage power source, at positive and at negative potential with respect to ground. Telephone central and subscriber exchanges can typically require several direct current voltage value ranges and polarity. It is technically and economically desirable to supply such power requirements from a minimum number of or a single storage battery source. A negative DC to positive DC converter can provide one simplifying and economical solution to this problem.
D. R. G. Cameron discloses in U.S. Pat. No. 3,522,510 issued Aug. 4, 1970 a DC to DC static converter suitable for generating from a storage battery source a voltage range output different from that provided by the battery. The battery voltage charges a capacitor, which is periodically alternately discharged from first and second halves of a transformer primary winding on a saturable magnetic core. The winding halves are series connected with SCR which are alternately triggered on pulses derived by a flip-flop driven by a unijunction oscillator. Means is provided to discharge the capacitor through the winding reducing the core saturation. The square wave voltage produced on the transformer secondary winding is rectified, filtered, and regulated to a satisfactory DC voltage output.
An earlier disclosure of a positive DC to positive DC voltage converter is contained in U.S. Pat. No. 3,470,446 issued Sept. 30, 1969 to E. H. Berry and F. J. Nola. The converter produces a lower DC positive voltage from a higher DC positive voltage across a load having a common voltage reference point. A plurality of capacitors are alternately charged by a DC source while in series, and then are discharged in parallel to a load having a common reference point with the DC source. Unidirectional conducting means are used to alternately connect the capacitors in series and then in parallel.
A still earlier disclosure of J. K. Mills discloses a power converter using switching transistors driven by an inductance-timed feedback network, in U.S. Pat. No. 3,179,901, issued Apr. 20, 1965. A plurality of transistor switches each directly connect a direct current source to a load. Each transistor switch is alternately switched into a nonconductive and a saturated conductive state by a feedback arrangement. A transformer primary winding is serially connected to the load and the secondary windings are arranged to drive the base electrodes of the transistor switches. An inductance is connected in parallel to the primary winding. The feedback device provides very rapid switching due to the ability to rapidly bring a saturated transistor out of saturation before switching is initiated.
R. F. Downs disclosed a DC to DC converter modification in EDN/EEE on Feb. 1, 1972, pages 48-50, which embodies inductances, thus introducing undesirable waveform transients.